The invention is directed to the mesylate trihydrate salt of 5-(2-(4-(1,2-benzisothiazol-3-yl)-1-piperazinyl)ethyl)-6-chloro-1,3-dihydr o-2H-indol-2-one (hereafter "ziprasidone mesylate trihydrate"), pharmaceutical compositions containing ziprasidone mesylate trihydrate, and methods of administering ziprasidone mesylate trihydrate to treat psychotic diseases. Ziprasidone is a potent psychotic agent and is therefore useful for treating various disorders including schizophrenia, migraine pain and anxiety. U.S. Pat. No. 5,312,925 refers to ziprasidone hydrochloride monohydrate, and states that ziprasidone hydrochloride monohydrate is substantially hygroscopically stable, which alleviates potential problems associated with weight changes of the active ingredient during the manufacture of capsules or tablets. U.S. Pat. No. 5,312,925 is herein incorporated by reference in its entirey. Ziprasidone hydrochloride monohydrate, however, has low aqueous solubility and, as a result, is more appropriate for capsule or tablet formulation than for injectable dosage forms.
Ziprasidone mesylate trihydrate also possesses hygroscopic stability. Ziprasidone mesylate trihydrate has the added advantage of having significantly greater aqueous solubility than the hydrochloride monohydrate, which makes the mesylate trihydrate more suitable for injectable dosage forms than the hydrochloride monohydrate. Further, of the four crystalline forms of ziprasidone mesylate, the mesylate trihydrate is the most thermodynamically stable in an aqueous medium at ambient conditions. This makes ziprasidone mesylate trihydrate advantageously suited for the preparation of consistent and precise dosage forms involving an aqueous medium.